在pom.xml的<dependencies></dependencies>标签下加入下面的依赖

<dependencies>    
    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.5.5</version>
    </dependency>
    <dependency>
        <groupId>commons-httpclient</groupId>
        <artifactId>commons-httpclient</artifactId>
        <version>3.1</version>
    </dependency>
</dependencies> 

然后点击界面右上角的重新加载maven

依赖库关系可以去官方网站找：仓库服务